Cut potatoes into 1-inch pieces.,Simmer in large pot of salted water 15 to 20 minutes, until potatoes are tender.,Drain.,While potatoes are draining, melt butter; add milk and salt and cook until hot.,Return potatoes to pot and mash, adding milk and butter.,Transfer to large shallow microwavable baking dish.,Cool; cover and refrigerate up to 2 days.,To serve, heat potatoes in microwave on high 20 minutes, stirring every 5 minutes, adding a little hot milk if potatoes seem dry.,______